Weapon cartridge

ABSTRACT

A cartridge for a small arms weapon, comprising a cover for housing a projectile; a metal cap at a rear end of the cover; a propellant charge located inside the cover at the rear thereof; and a gas seal element located inside the cover adjacent to the propellant charge and having an annular sealing formation projecting rearwardly towards the propellant charge and being outwardly deformable on detonation of the propellant charge for sealing against an internal surface of the cover. The metal cap has a rim extending longitudinally over a portion of the external surface of the cover for supporting the cover where the sealing formation first seals against its internal surface.

The present invention relates to a cartridge for a small arms weapon having a barrel, such as a shotgun, and in particular a cartridge having an improved gas seal.

Known cartridges for small arms weapons comprise a tubular plastic cover which houses a projectile and its firing package. The firing package includes a propellant charge and a plastic or fibre wad which acts as a gas seal between the propellant charge and the rear of the projectile. A brass cap or head is formed at the rear of the plastic cover and is used to hold a primer in alignment with the propellant charge. The width of the rim of the brass cap is also used to differentiate between different types of ammunition. When the weapon is triggered, a firing pin strikes the primer at the centre of the cap's rear surface, which in turn detonates the propellant charge. The expanding gases rush forward into the wad, which then forces the projectile forward, out of the plastic cover and through the weapon's barrel.

Such projectiles display variation in their range and accuracy between different rounds. To some extent, this variation is tolerated. However, as longer ranges are achieved, consistency is often reduced. Therefore, as demand for ever more powerful, longer range projectiles increases, there is a need to find ways to reduce variation between rounds and improve consistency.

The present invention seeks to address the above issues.

According to an aspect of the present inventions there is provided a cartridge for a small arms weapon, comprising:- a cover for housing a projectile; a metal cap at a rear end of the cover; a propellant charge located inside the cover at the rear thereof; and a gas seal element located inside the cover adjacent to the propellant charge and having an annular sealing formation projecting rearwardly towards the propellant charge and being outwardly deformable on detonation of the propellent charge for sealing against an internal surface of the cover; wherein the metal cap has a rim extending longitudinally over a portion of the external surface of the cover for supporting the cover where the sealing formation first seals against its internal surface.

In this way, on detonation of the propellant charge, the sealing formation of the gas seal is forced outwardly into engagement against the interior surface of the plastic cover. At the same time, the counterpart outer surface of the plastic cover is braced by the rim of the metal cap, thereby preventing it from rupturing. That is, the rim of the metal cap extending along the rear of the cover performs a functional role, supporting the plastic cover and allowing it to be compressed between the distal edge of the sealing formation and the cap rim. This forms a tight and consistent gas seal around its circumference, with the improved seal preventing the expanding propellant gases from rupturing the cover or leaking past the rear of the projectile. This ensures a more efficient and even delivery of the propellant forces over the rear surface of the gas seal, which thereby maximizes the forward momentum delivered to the projectile. Furthermore, as the gas seal more evenly distributes the propellent forces, the projectile will more likely adopt a zero angle of attack when leaving the barrel and thereby maintain aerodynamic symmetry during flight. As such, the projectile is provided with an improved range for a given quantity of propellant charge, and there is a lower standard deviation in exhibited ranges and greater accuracy between rounds.

Preferably, the sealing formation is inclined radially outward. In this way, the sealing formation is configured to deform outwardly.

Preferably, the gas seal element has a disc shaped body. In this way, the body of the gas seal can occlude the majority of the internal bore of the cover. This minimizes the deformation required to allow the sealing formation to form the tight seal against the internal surface of the cover.

Preferably, the gas seal element further comprises a notch at a base of the sealing formation for directing its deformation outwardly. In this way, the gas seal element is configured to promote the outward deformation of the sealing formation.

Preferably, the notch is formed on a circumferential surface of the disc shaped body.

Preferably, the gas seal element further comprises a formation for receiving the rear of a projectile. In this way, alignment between the projectile and the gas seal is easily achieved.

Preferably, the cartridge further comprises a projectile at least partially received inside the cover. In this way, a complete packaged weapon cartridge is supplied, which can be inserted directly into a small arms weapon's barrel.

Preferably, the cover is formed of a plastic material, such as ultra-high molecular weight polyethylene.

Preferably, the metal cap comprises brass. The malleability and low friction properties of brass facilitate the loading and movement of the cartridge in the weapon's barrel with minimal risking of sparking. At the same time, the provision of a high brass shell or rim, which extends beyond where the sealing formation contacts the cover, provides sufficient support to prevent rupturing of the cover material.

Preferably, the rim of the metal cap extends beyond the longitudinal position where the sealing formation projects from the gas seal element's body.

Preferably, the sealing formation defines a central depression in the rear surface of the gas seal element.

Preferably, the propellant charge is at least partially received into the central depression.

Preferably, the central depression has a cone shaped profile for directing expanding gases radially outward toward the inward facing surface of the sealing formation. In this way, the expanding gases are directed outward into the sealing formation, forcing it outward.

Preferably, the rim of the metal cap extends to a longitudinal position between the front of the gas seal element and the position where the sealing formation projects from the gas seal element's body.

According to a further aspect of the present invention, there is provided a cartridge comprising: a plastic casing having a metal cap formed over one end for forming a supported region inside the casing; a propellant charge provided inside the casing, adjacent to the metal cap; and a gas seal located inside the casing and having a rearward surface comprising a circumferential wall projecting toward the propellant charge; wherein the circumferential wall is configured to deform outwardly on detonation of the propellant charge for contact with the supported region of the casing so that the supported region of the casing is compressed between a distal edge of the circumferential wall and a rim of the metal cap.

The invention will now be described, by way of illustration only, with reference to the accompanying drawings in which:

FIG. 1 shows a cross sectional view of a cartridge according to an embodiment of the invention;

FIG. 2 shows a rear view of the gas seal shown in FIG. 1; and

FIG. 3 shows an expanded cross sectional view of the rear of the cartridge immediately after detonation of the propellant charge.

FIG. 1 shows a cross sectional side view of a cartridge housing a projectile 9. The cartridge comprises a plastic cover or casing 1 with a brass cap or head 5 cast over its rear end. The brass cap holds the primer 10 and has a rim 6 which extends longitudinally along the sides of the plastic cover 1 creating a region inside the cap 5 where the plastic cover is supported. The projectile 9 is housed inside the plastic cover 1, ahead of disc shaped gas seal 2 and propellent charge 4.

The gas seal 2 comprises a body with an annular rim 8 formed on its front surface and into which the rear of the projectile 9 is seated. The gas seal body is provided with an annular sealing formation 3 projecting rearward and outwardly at an incline from the rearward facing surface of the gas seal body. Notch 7 is also provided on the outer circumferential surface of the gas seal body, at the joint between the body and the sealing formations 3. This notch or groove 7 forms a stress concentrator for focusing the deformation of the sealing formation outwardly at the joint.

FIG. 2 is a view of the rear of the gas seal 2. The gas seal 2 has a tubular shape with a diameter substantially identical to the internal bore of the tubular cover 1. The annular sealing formation 3 forms an outwardly inclined circumferential wall around the periphery of the gas seal 2, with a central depression into which the propellent charge 4 can be at least partially received. As such, the rear of the gas seal has a shallow dish-like profile. As shown in

FIG. 1, in this embodiment, the central depression also has a shallow cone like profile with a central apex and inclined surfaces tapering outwardly. This shape acts to direct expanding gases radially outward, toward the sealing formation 3, thereby promoting its deformation outward. The shape also helps to achieve an even distribution of propellant forces over the rear of the gas seal 2.

In use, the cartridge with a pre-installed projectile is loaded into a small arms weapon's barrel. When the firing pin strikes the rear surface of the metal cap 5, it fires the primer 10, which in turn detonates the propellant charge 4. On detonation, there is an explosive expansion of propellant gases.

As the propellant gases move forward, they apply pressure to the rear surface of the gas seal 2. The expanding gases also act against the inward facing surfaces of the sealing formation 3, which forces it to bend outward at notch 7. This moves the distal edge of sealing formation 3 to press against the plastic cover 1. However, as the high rim 6 of metal cap 5 extends longitudinally past this point of contact, the sealing formation 3 is within the supported region of the plastic cover 1 such that the contacting area is braced by the rim 6. This allows the sealing formation to compress the plastic cover 1 without rupturing it. FIG. 3 shows an enlarged view of this.

This compression of the plastic cover 1 between the rim 6 and sealing formation 3 forms an effective seal around the circumference of the gas seal 2. This prevents the expanding gases from leaking past the rear of the gas seal 3 which could otherwise result in pressure loss or lateral forces being applied to the projectile 9. As such, the maximum propulsive force is delivered to the projectile in a forward direction for propelling the projectile 9 out of the plastic cover 1 and the weapon's barrel. Furthermore, the gas seal 2 ensures a more even distribution of forces to the rear of the projectile 9. Not only does this allow for more efficient use of the propellent charge 4, but also greater consistency between rounds. These advantages therefore allow for improved accuracy and less variation between rounds.

It will be understood that the embodiment illustrated above shows an application of the invention only for the purposes of illustration. In practice the invention may be applied to many different configurations, the detailed embodiments being straightforward for those skilled in the art to implement. 

1. A cartridge for a small arms weapon, comprising: a cover for housing a projectile; a metal cap at a rear end of the cover; a propellant charge located inside the cover at the rear thereof; and a gas seal element located inside the cover adjacent to the propellant charge and having an annular sealing formation projecting rearwardly towards the propellant charge and being outwardly deformable on detonation of the propellent charge for sealing against an internal surface of the cover; wherein the metal cap has a rim extending longitudinally over a portion of the external surface of the cover for supporting the cover where the sealing formation first seals against its internal surface.
 2. A cartridge according to claim 1, wherein the sealing formation is inclined radially outward.
 3. A cartridge according to claim 1, wherein the gas seal element has a disc shaped body.
 4. A cartridge according to claim 1, wherein gas seal element further comprises a notch at a base of the sealing formation for directing its deformation outwardly.
 5. A cartridge according to claim 1, wherein the gas seal element has a disc shaped body and further comprises a notch at a base of the sealing formation for directing its deformation outwardly, wherein the notch is formed on a circumferential surface of the disc shaped body.
 6. A cartridge according to claim 1, wherein the gas seal element further comprises a formation for receiving the rear of a projectile.
 7. A cartridge according to claim 1, further comprising a projectile at least partially received inside the cover.
 8. A cartridge according to claim 1, wherein the cover is formed of a plastic material.
 9. A cartridge according to claim 1, wherein the metal cap comprises brass.
 10. A cartridge according to claim 1, wherein the rim of the metal cap extends beyond the longitudinal position where the sealing formation projects from the gas seal element's body.
 11. A cartridge according to claim 1, wherein the sealing formation defines a central depression in the rear surface of the gas seal element.
 12. A cartridge according to claim 11, wherein the propellant charge is at least partially received into the central depression.
 13. A cartridge according to claim 11, wherein the central depression has a cone shaped profile for directing expanding gases radially outward toward the inward facing surface of the sealing formation.
 14. A cartridge according to claim 1, wherein the rim of the metal cap extends to a longitudinal position between the front of the gas seal element and the position where the sealing formation projects from the gas seal element's body.
 15. A cartridge comprising: a plastic casing having a metal cap formed over one end for forming a supported region inside the casing; a propellant charge provided inside the casing, adjacent to the metal cap; and a gas seal located inside the casing and having a rearward surface comprising a circumferential wall projecting toward the propellant charge; wherein the circumferential wall is configured to deform outwardly on detonation of the propellant charge for contact with the supported region of the casing so that the supported region of the casing is compressed between a distal edge of the circumferential wall and a rim of the metal cap. 